446 F. W. GAMBLE AND J. H. ASHWORTH. 



faint oblique striations are occasionally visible (fig. 12 b). 

 Each notopodial pencil contains only one seta of the latter 

 kind, accompanied by three, four, or five of the normal 

 plumose setae (PI. 24, fig. 34). 



Mesnil (1897) found these two kinds of setse in the noto- 

 podia of a small polychrete, which he then identified with 

 Clymenides sulfureus, Clapar&de. On comparing the 

 post-larval stages of A. marina in our possession with 

 Mesnil's descriptions and figures of this polychrete we have 

 no doubt that his Clymenides is nothing but a post-larval 

 A. marina, and in a later paper Mesnil (1898) has arrived 

 at the same conclusion. 



The notopodial sette of post-larval specimens of A. ecau- 

 data are also somewhat difi^erent from those of the adult. 

 Thus in a specimen 7'2 mm. long they are *25 mm. to '3 mm. 

 long, and bear a distinct lamina on one side of the distal third 

 or half of their length. The lamina is divided into two 

 portions, a short proximal part devoid of hairs, and a longer 

 distal part, on the greater portion of which distinct hair-like 

 processes may be seen (fig. 21), while between the two seta 

 is slightly constricted. Setfe identical with these were 

 described by Mesnil (1897) from a small polychaete to which 

 he gave the name Clymenides ecaudatus. On the pub- 

 lication of MesniFs paper we at once identified his speci- 

 mens with our post-larval specimens of Arenicola ecaudata 

 obtained in August, 1896, to which conclusion Mesnil has also 

 arrived in his later paper (1898). 



The most remarkable feature noticeable in the sette of 

 young specimens of A. ecaudata is one to which Mesnil has 

 also drawn attention, viz. that a crotchet indistinguishable 

 from those of the neuropodia occurs in some of the posterior 

 notopodia alongside the ordinary capilliform sette. In the 

 posterior portion of a specimen 8 mm. long we find a 

 crotchet in the notopodium in each of the last six segments 

 which bear notopodial setae, i. e. in the last formed or young- 

 est segments (PI. 24, fig. 37). In the last and the last but 

 two notopodia the crotchet stands alone, but in the others 



